The present invention is directed to an improved suture ring for a heart valve and a method of securing the suture ring to the heart valve.
The majority of artificial atrial and mitral heart valves implanted in humans are fabricated from carbon coated with another form of carbon known commercially as pyrolite. Pyrolytic carbon is employed because of its unusual non-thrombogenic properties. Human blood does not readily coagulate on contact with it and it is lightweight, hard and quite strong.
These implantable mechanical heart valves are formed with a circular or eliptical valve housing or body providing a blood flow passageway. Occluder means are mounted on the valve body for opening and closing the blood flow passageway. The physical configuration of the occluder means or valve, generally, is one of a flap, butterfly or leaflet design. The valve body, in turn, has an external, circumferential surface, usually configured as a groove, formed around the valve body. The purpose of the groove is to facilitate attachment of a suture ring to the valve body.
In all cases, the heart valve is attached to the patient's heart tissue by suturing the heart tissue to the suture ring attached to the heart valve. The suture ring generally comprises a knit fabric, typically Dacron, tube rolled into a toroidal form which is secured about the heart valve body in the aforementioned circumferential groove. One known method for securing the suture ring to the carbon valve body of the heart valve involves binding the suture ring into the external circumferential groove of the valve body with a plastic thread. The assembly of the suture ring and valve body is then heat-treated to cause the plastic thread to shrink and firmly secure the suture ring to the valve body.
A major drawback with the assembly of the heart valve and suture ring which are secured together with the aforementioned known technique is the inability to adjust the location of the heart valve with respect to the suture ring after suturing the heart tissue to the suture ring of the assembly. This is significant because of the necessity of optimizing the axis of the valve relative to the patient's heart chamber.
With known suture rings, where the suture rings are secured to the heart valve during the fabrication of the suture rings, there is also the additional disadvantage that a close inspection of the suture ring to ascertain its integrity prior to committing the suture ring to an expensive heart valve is not possible. The processing of the completed suture ring as by coating the suture ring with a non-thrombogenic coating, e.g. Biolite, is also disadvantageous in that it requires masking of the heart valve attached to the suture ring to protect the valve.
While there have been proposals for forming a rotatable suture ring on a heart valve using heat shrinkable plastic material, as in U.S. Pat. No. 3,781,969, for example, with such techniques, it can be difficult to repeatedly obtain uniform contracting and holding forces, and thus accurately control the required torque, for relative rotation between the suture ring and the valve. Furthermore, there is no opportunity for close inspection of a completed suture ring to ascertain its integrity prior to assembling the suture ring on the heart valve, the heart valve must be masked to protect it during further processing of the suture ring such as non-thrombogenic coating thereof and the heart valve is subject to thermal exposure during the heat shrinking of the plastic material which can possibly damage the valve.
It has also been proposed to initially form the suture ring as a separate sub-assembly which is then attached to the heart valve. In U.S. Pat. No. 3,491,376, for example, the suture ring includes a resilient annular member which is temporarily deformed, so as to snap the interior portion of lesser diameter of the annular member into juxtaposition with the exterior portion of larger diameter of the valve body. It is also known to use metal snap rings as in U.S. Pat. No. 3,579,642, for example, which must be radially expanded to place the suture ring about the valve body. However, with such fabrication techniques, there is the risk of potential damage to the suture ring when the ring is mechanically, radially expanded in placing it about the valve body. For example, where the suture ring is radially expanded by forcing it over a flange to one side of the circumferential groove of the valve body for positioning the suture ring opposite the groove of the valve body, there is the danger of damage to the fabric of the suture ring and also the possibility a loose fit of the suture ring on the valve body once the ring is in position adjacent the groove. This loose relationship is undesirable as in use the valve may shift or slide relative to the suturing member and blood accumulate and stagnate the adjacent valve.
An object of the present invention is to provide a method of securing a suture ring to a heart valve which avoid the aforementioned disadvantages of the known suture rings and methods of securing the same to heart valves.
More particularly, an object of the present invention is to provide method of securing a suture ring to a heart valve which allows the heart valve to be rotated in vivo with respect to the suture ring by applying sufficient torque to the valve body without causing excessive tension on the sutures connecting the heart tissue with the suture ring and without an undesirable amount of looseness existing between the suture ring and valve body.
A further object of the invention is the provision of a method of securing a suture ring to a heart valve which permits very accurate control of the torque required for relative rotation between the valve body and the suture ring, which result can be repeatedly accomplished during manufacture in a simple manner.
A further object of the invention is the provision of a method of securing a suture ring to a heart valve which permit the fabrication of the suture ring as a separate sub-assembly before securing the suture ring to the heart valve body thereby allowing close inspection of the suture ring to ascertain its integrity prior to securing the suture ring to the heart valve, and which permit the suture ring to be processed independently of the heart valve to avoid masking of the heart valve, for example, where it is desired to provde a non-thrombogenic coating on the completed suture ring.
An additional object of the invention is to provide a method of securing a suture ring to a heart valve which minimizes the potential risk to the suture ring during securing of the ring to the heart valve by eliminating the need for forceably radially expanding the suture ring during positioning of the ring about the valve body and by eliminating the need for heating the suture ring and heart valve during their assembly.
These and other objects of the invention are obtained by the suture ring of the invention which includes a continuous compression ring formed of a ductile, electrically conductive material and a layer of fabric secured around the compression ring, the compression ring being dimensioned slightly larger than the circumferential surface of the heart valve upon which it is to be secured so that the suture ring can be slipped over the heart valve to a position adjacent the circumferential surface without necessitating a forced radial expansion of the compression ring.
The conductive compression ring forms a closed electrically conductive loop which has an electrical resistance of less than 15 .mu. ohm/cm. The ductility of the electrically conductive compression ring is also at least equal to the ductility of pure iron and the ring is formed so that it is bio-compatible. For example, the compression ring can be made of a material which is bio-compatible or merely coated with a material which is bio-compatible.
As illustrated in the disclosed, preferred embodiment of the invention, the shape of the radially inwardly facing surface of the compression ring is substantially the same as the shape of the external, circumferential surface of the heart valve to which the suture ring is to be secured. At least one layer of fabric is secured around the entire external surface of the compression ring to form a completed suture ring prior to securing the suture ring on the heart valve. This permits the suture ring to be closely inspected to ascertain its integrity prior to securing the suture ring on the heart valve. Additional processing of the completed suture ring sub-assembly such as by coating with a non-thrombogenic coating of Biolite, for example, can also be accomplished without masking the heart valve or otherwise subjecting it to possible damage during such processing.
The method according to the invention of securing a suture ring to an implantable heart valve comprises the steps of providing a continuous, ductile, electrically conductive compression ring of the suture ring which is dimensioned slightly larger than the circumferential surface of the heart valve body, positioning the electrically conductive compression ring about the valve body so that it faces the external, circumferential surface of the valve body to which the suture ring is to be secured, and electromagnetically deforming the conductive compressive ring, so that it securely clamps the circumferential surface of the valve body. The fabric layer of the suture ring is interposed between the compression ring and the circumferential surface of the valve body and becomes clamped therebetween during the electromagnetic deformation of the compression ring.
The electromagnetic deformation of the compression ring of the suture ring is accomplished by placing the suture ring located opposite the circumferential surface of the valve body within a magnetic field generator which momentarily generates a magnetic field about the entire closed loop of the conductive compression ring. This induces an electromagnetic impulse current within the conductive compression ring resulting in a uniform inwardly directed radial force which deforms the compression ring inwardly to cause it to securely clamp the circumferential surface of the heart valve body. For example, the compression ring can be caused to nest within a circumferential groove of the heart valve body or to hug a protrusion on the circumferential surface. In either case, the compression ring is caused to securely clamp the valve body over at least a major portion of the axial length of the compression ring to prohibit axial shifting of the ring on the valve, while permitting relative rotational movement of the heart valve body and the suture ring in a direction along the circumferential surface of the heart valve body thereby permitting adjustment of the heart valve with respect to the suture ring after the valve has been sutured to a patient's heart tissue. The degree of deformation of the compression ring is accurately controlled, so as to precisely and repeatedly control the torque necessary to rotate the heart valve with respect to the suture ring without undesirable looseness existing between the suture ring and valve body.
The method of securing the suture ring to the heart valve body via the compression ring permits fine control of the torque necessary to cause relative rotation of the heart valve and the suture ring without necessitating forced radial expansion of the ring during the securing operation which can damage the suture ring. The method is further advantageous in that the forming of the compression ring by electromagnetic impulse generates no significant heat, so that the suture ring and the heart valve are not subjected to possible thermal damage.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.